Switch and speed control mechanism utilizing variable resiliency spring means



Feb. 24, 1970 J GREEN, JR 3,497,650

SWITCH AND SPEED CONTROL MECHANISM UTILIZING VAHIABLE'RESILIENCY SPRING MEANS Filed April 25, 1968 2 Sheets-Sheet 1 v1 2 H /1 iii; 2

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50. v Inventor- James Green Jr Attorney J. GREEN, JR 3,497,650 SWITCH AND SPEED CONTROL MECHANISM UTILIZING Feb. 24, 1970 VARIABLE RESILIENCY SPE-ING MEANS 2 Sheets-Sheet 2 Filed April 25, 1968 [/7 we far James Green (/n United States Patent SWITCH AND SPEED CONTROL MECHANISM UTILIZING VARIABLE RESILIEN CY SPRING MEANS James Green, In, Spencerport, N.Y., assignor to General Electric Company, a corporation of New York Continuation-impart of application Ser. No. 660,757, Aug. 15, 1967. This application Apr. 25, 1968, Ser. No. 730,972

Int. Cl. H01h 35/10 U.S. Cl. 200-80 7 Claims ABSTRACT OF THE DISCLOSURE The disclosure herein shows an improved switch and speed control mechanism utilizing variable resiliency spring means that is for use in an electric power tool such as a food mixer and having novel structure to provide accurate low speed control when the mixer is in operation.

BACKGROUND OF THE INVENTION Field of the invention The invention herein is a continuation-in-part replacing application Ser. No. 660,757, now abandoned, filed Aug. 15, 1967, and pertains to a switch and speed control mechanism for an electric power tool such as a food mixer and, more particularly, to a novel mechanism that uses a unique dual cam governor control structure to provide for accurate low speed operation by having a spring operating in combination with other structure to provide better spring action through the speed range and a modification to provide variable spring action at low speeds and solid link action at higher speeds.

Description of the prior art In the small appliance field, and especially in portable food mixers, it is desirable to have the various control units as convenient as possible for the use for operation of the mixer by either hand. There are two main controls that govern the operation of the mixer and these are the speed control and the beater ejector mechanism. It is desirable to provide both controls operable conveniently from either side of the mixer by the hand of the user when holding the mixer. Thus, a concentric and centrally disposed arrangement is suggested. This comprises a speed control selection knob centrally disposed on the handle at the top with an inner ejector knob so that either a right or left handled person can control the speed selection knob with his index finger or thumb and eject the beaters with his thumb. In addition, it is desirable that the beaters not be ejected while the mixer is in operation for safety purposes. A structure for attaining beater ejection consistent with these objective is disclosed in U.S. Patent 3,- 443,795, dated May 13, 1969 and of common assignment. Additionally, it is desirable to provide a speed control mechanism that utilizes as much of the common structure as possible and provides for operation over a Wide range of speeds. Generally, such speed controls comprise a flyweight governor system mounted on a rotatable shaft and a force balancing control spring operating in conjunction therewith to rapidly make and break the motor circuit to cause the motor to operate at a selected speed. The flyweights develop a force proportional to the speed of shaft rotation and move an actuator axially to cause a cantilevered arm carrying one of the circuit contacts to open the energizing circuit.

The cantilevered arm is biased by the control spring in a direction opposed to the flyweight force such that the force developed by the control spring determines the actuator force needed to pivot the cantilevered arm to momentarily de-energize the circuit. A linkage between the control knob and the governor control spring provides the means for varying the governor control spring force by cam action or other suitable means to achieve the desired speed.

The flyweight force and the governor control spring force balance one another to maintain the selected speed. Because of the present day need for a wide range of speeds, it is difiicult to provide a control spring mechanism capable of producing the low level control forces required for slow speed operation and the high level control forces required for high speed operation. It is desirable to provide a compact dual cam and switch arrangement with a spring control mechanism that will provide accurate control over the complete speed range and, in a modified form provide more accurate control in the low speed range and still be capable of developing the high force needed for high speed operation and it is to these ends that the present invention is directed.

SUMMARY OF INVENTION Briefly described, the present invention is directed to the combination an electric food mixer which has a casing and a power unit including a spring force balancing governor system with a driven spindle controlled by said system and having a make-break switch actuated by the spindle. To this basic system the invention proposes an improvement of a switch and speed control mechanism which comprises a rotatable speed control shaft that has two functions which are to both actuate the control system and an on-otf switch mechanism. Cam means are provided on the shaft which may take the form of two separate cams or a single cam with two separate cam surfaces thereon and these forms are used and intended interchangeably herein. A resilient cam follower is actuated from a neutral or pre-set position by the first cam surface on shaft rotation. A governor control spring is attached to the cam follower and a pivoted arm forms part of the governor system such that rotation of the speed control shaft causes cam follower displacement either to increase or decrease the spring force thereby controlling speed. Means are also provided in a modification in conjunction with the dual cam structure forming part of the control spring to change the control spring force whereby a variable control spring force is applied to the governor system at low speeds and a solid or non-resilient link is applied at predetermined shaft rotation to hold the governor contacts closed thus achieving maximum speed. In addition and concurrently, the second cam surface, which is axially and angularly displaced from the first cam surface, independently actuates a biased on-ofif switch which energizes or de-energizes the power unit circuit. Suitable means provides a holding force to keep the switch in the open or off position. The invention may use a bracket secured the casing which bracket forms a support for the speed control shaft and the cam means may form the support for the shaft directly on the bracket. Additionally, in the modified form the spring means may be a helical spring with a take-up linkage for the spring to stretch a predetremined amount and then have its coils by-passed to form a solid non-resilient link. The means for operating the switch means may take the form of an insulated slider contacted by the second cam surface and directly operating the switch to a closed position when the speed control shaft is rotated out of the neutral or stop position.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is an elevational side view partially broken away to illustrate a food mixer with the invention;

FIG. 2 is a partial top sectional view on the line 22 of FIG. 1;

FIG. 3 is a perspective view of a modification of the switch and speed control mechanism showing some parts in an exploded position;

FIG. 4 is a partial view of the FIG. 3 modification showing the speed control shaft rotated to another position; and

FIG. 5 is a partial view of the FIG. 3 modification showing the speed control shaft in still a different position.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring first to FIGS. 1 and 2 there is shown a food mixer indicated at that is generally made up of two mating casing 12 and 14 for convenience. Upper casing 12 is provided with a handle 16 and the mixer is designed to be tilted on its handle when not in use. In order to operate the mixer, there is provided a power unit 18 that drives a spindle proportional to the speed. Spindle 20 extends between a pair of adjacent gears 22. A pair or more of heaters 24 are provided with beater shafts 26. Each of the gears 22 has a central aperture 28 which receives shafts 26 therethrough and the beater shafts 26 are held in position in the mixer by suitable means. The novel ejector mechanism and operation thereof is completely described in the referenced copending application.

In order to provide a mechanism which uses as much of the common ejector mechanism present as well as proyiding a fail-safe switch-off feature during ejection and a speed control mechanism that is accurate over the range of mixer speeds and is compatible with the ejector so that the heaters cannot be ejected when the mixer is running, it is necessary to provide spring means to permit a variable balancing force on the governor system. Any spring mechanism that is sufiiciently flexible to balance the governor forces is adequate. A coil spring to balance a fly ball governor is known and such a spring may be used in combination with the remaining unique control mechanism using a dual cam and switch arrangement to be described to provide the necessary speed control. A modification of such structure may use a different spring arrangement to provide a more closely adjusted speed control that changes its resisting force over the speed range. Such a modification provides more accuracy at low mixer "speeds by permitting a variable balancing force on the governor system at low speeds and a non-variable or nonresilient solid link structure at higher speeds. Generally, a constantly variable spring mechanism that is sufiiciently flexible to balance the governor forces at low speeds may not have the desired rigidity at high speeds with the result that accurate low speed operation may not be all that is desired by the use of conventional and existing springs. This means that the low speed ranges as may be used in certain whipping operations in a mixer may not be completely accurate. One of the reasons is that the very inertia of the mechanism itself does not permit the completely desired accurate control on the low speed ranges. A pivoted actuating arm in the invention to operate a. make-break switch reduces such inertia to provide better control. Thus, the switch and speed control mechanism of the instant invention uses a different control rod-dual cam and switch arrangement to control speed and prevent beater ejection while running as well as a modification of the spring structure in the same combination which applies a variable balancing force at low speeds and a nonvariable or nonresilient solid link structure on the governor at higher speeds. Both systems, except for the spring, operate substantially the same and, only one need be described. To avoid dual description, the modified arrangament using the variable and solid link structure spring shown in FIGS. 4 and 5 will be described and it will then be apparent how the continuously variable spring arrangement of FIGS. 2 and 3 operates.

In a food mixer it is desirable to have a force balancing governor system generally indicated at 30 in FIG. 2. This usually comprises a mechanism 32 that may take numerous forms and, for convenience, is termed a flyweight mechanism which operates through actuator cap 34 which actuates a normally cantilevered arm 36 to operate contact 38 to make and break the electrical circuit and control the speed in a generally known manner. Different speeds are provided as seen in FIG. 2 by varying a spring force on arm 36 by means of spring 39 that is connected to a resilient cam follower 42 which, in the present invention, operates in a novel manner as will become apparent. The governor system just described with a conventional spring 39 is generally known except as it may form part of the present switch and speed control mechanism.

Referring now to the modifier form of FIG. 3 which will be described, it will be seen that in order to provide speed variation, a rotatable speed control shaft 44 is disposed so as to extend out of the mixer handle and be rotatable under control of knob 46 to vary the speed by changing the spring force on arm 36. The shaft 44 is generally parallel with beater shafts 26 so that it preferably extends vertically to the plane of rotation of gears 22 and upward through the handle 16 and is rotatable at the top front of the handle as seen in FIG. 1. Support for the rotatable shaft 44 may be provided by means of a bracket 48 that is 'supported within the casing conveniently as part of the bearing structure 50 for one end of the power unit. The whole bracket and bearing structure may be secured to suitable bosses in the casing (not shown) by single screws 52. Bracket 48 is shaped to extend over the gears 22 as shown in FIG. 3 and it forms the bottom support for the rotatable speed control shaft 44. The support in the bracket is provided by a switch control cam means indicated at 54 on one end adjacent and above the bracket as shown. The cam means is designed to anchor and limit axial movement of the shaft 44 in the bracket and thus support the shaft in addition to performing its dual cam duties.

Cam means 54 may be formed in two parts or as a single cam with dual spaced and separate first and second cam surfaces 56 and 58, respectively, as best seen in FIG. 3. The structure will be described by the first and second cam surfaces although it will be apparent that these might be separate adjacent cams. It can be seen that rotation of knob 46 turns first cam surface 56 against resilient cam follower 42 to change force through spring 40 connected between follower 42 and arm 36. The amount of spring force thus exerted against arm 36 is dependent on the position of first cam surface 56 contacting follower 42 and changing the force required by actuator 34 to make and break contacts 38. Since accurate control at low speeds is more diflicult due to the inertia of the system and the requirement that spring 40 be fully operable over the entire low speed range, it is desired to reduce the inertia in the system and to this end, arm 36 is disposed to rotate about pivot 60 so that resistance to rotation or inertia movement of arm 36 is extremely low. This means that spring 40 is immediately reactive on arm 36 without using some of its restoring force to bend the usual cantilever type arm 36. Thus, substantially no resistance is offered by arm 36. In order for the follower 42 to contact first cam surface 56 it is desired that the follower be resiliently connected as by the cantilever connection shown. This may conveniently be made on an upstanding portion of bracket 48 as shown. When the device is in the off position, as will be explained, the cam surface 56 does not actuate follower 42 and it is thus in its neutral or off position. The off feel is obtained by a flexible detent 57 operated in the casing in a known manner. Thus rotation of knob 46 actuates follower 42 from its neutral position by the first cam surface 56. As rotation of shaft 44 continues for higher speeds, first cam surface 56 moves follower 42 farther away from arm 36 and applies more force through spring 40 with the result that con= tact 38 is not broken until higher speeds are attained. Then by rapid making and breaking, the speed is maintained by the force of the balancing governor system. As previously noted, accurate control at low speed is more difficult to attain and to this end, the modification of the invention herein also discloses a novel spring structure 40 which contains means forming part of the spring to change the spring force from a variable spring force to a solid non-resilient link at a predetermined shaft rotation. This may be provided by several means such as by looping the spring back upon itself in a helical spring as shown in FIG. 3 so that a projection 62 will, after predetermined travel, contact the loops of the helical spring and render them inactive whereby a constant link connection between follower 42 and arm 36 is provided. Additionally, a take-up mechanism using a ban 64 as shown in FIG. 5 may be used. The band merely floats freely at low extensions of the spring and contacts the loops as the spring is further extended to eventually render it a solid link to maintain the make and break contacts 38 closed at higher speeds. Other forms will readily suggest themselves whereby the spring is variable at low rotation of shaft 44 and low speed and becomes a solid link on further shaft rotation and higher speed. Thus, the counter force applied to arm 36 is variable at low speeds and constant at the higher speeds. In both spring forms 39 and 40, the spring force is thus fully exerted by pivoted arm 36 on the makebreak switch at low speeds and is increased at higher tool speeds.

In order to provide an off position of the power unit, and to provide this in the neutral position of follower 42, cam means 54 makes use of its second cam surface 58 which surface is axially and angularly displaced from the first cam surface 56 for a purpose to be described. A switch means 66 is provided in the power unit circuit to additionally control the on-olf condition of the circuit. The switch means 66 is operable by a second cam follower 68 that conveniently takes the form of an inslider 68 to closed position at contacts 70. In order that sulated slider disposed on the surface of bracket 48 so that it slides in a plane parallel thereto by any suitable connection as moved by the second cam surface 58. Switch means 66 may take the form of a cantilever leaftype spring that is normally biased against the end of the slider 68 may be operated independently by the second cam surface 58, a suitable aperture or opening 72 may be provided in follower 42 so that surface 58 slides under follower 42 and has no action on it. Thus, slider 68 is operated independently to control the power unit circuit. The angular displacement of the cam surfaces 56 and 58 is such that switch means 66 is open and the motor OK when the resilient cam follower 42 is in its neutral position and on or closed at other times. This position is the off position of the mixer held by detent 57 and the switch means then controls the circuity. As will be apparent from the co-pending application, this position is desired also for the beater ejector mechanism which uses in common much of the speed control shaft structure 44 herein. Different positions of higher speed operation are shown in FIGS. 4 and 5 where the second cam surface 58 has rotated under follower 42 but is not affecting it and switch 66 is then closed and the motor circuit is on.

The operation of the device will be apparent. In the off or neutral position of follower 42, switch means 66 is open to break the circuit and this is obtained by second cam surface 58 actuating slider 68 to break the contact 70. Upon further rotation of shaft 44 out of detent 57 the second cam surface 58 passes out of contact with slider 68 whereupon the resilient switch means 66 closes and energizes the circuit. Continued rotation brings first cam surface 56 into contact with follower 42 to move its end as shown by the arrow in FIGS. '4 and 5 to vary the spring force in spring 40 and operate the setting of the governor as in FIG. 4. This spring force continues variably throughout the entire speed range to apply more force on the make-break contacts 38 at higher tool speed with spring 39 of FIG. 2 and also, in the modification of FIGS. 3-5 continues in the normal fashion until projection 62 or its equivalent band 64 restricts the further extension of spring 40 as in FIGS. 3-5. This may occur at any predetermined shaft rotation as designed. When this occurs spring 40 becomes a solid link tending to hold contacts 38 in closed position whereupon the mixer operates at full motor speed. The reverse rotation of shaft 44 permits spring 39 to variably back off and the modified spring 40 to back off as a link and then become effective as a spring in the lower speed ranges to provide accurate governor control of the speeds in the lower ranges. Neither spring is affected by internal friction or inertia due to the pivoting arrangement of arm 36 which it moves freely at all times.

Thus, the switch and speed control mechanism described permits the spring force to act fully on the movement of arm 36 and provide accurate control over the entire speed range and variable control over at least part of the speed range. Additionally, the two-cam structure supporting shaft 44 and its connected switch structure operates to provide a switch control on the power unit that is independent of the governor position that determines speed except in the off position. While any suitable rotational positions may be selected, in the modified spring 40 it is desired to have good spring control in the lower ranges and, as an example, the spring may be active up to 200 or three quarters of a turn of the shaft 44 before it becomes a non-resilient solid link. This is not a limiting factor by any amount of rotation can be obtained for settings of the continually variable spring 39 or by the take-up structure in the spring 40 which effectively deactivates the spring as a spring in the higher speed ranges. Thus, other modifications may be made without departing from the scope of the invention as described in the claims.

I claim:

1. In an electric power tool such as a food mixer having a casing and a power unit therein including a spring force balancing governor system with a driven spindle controlled by said system and having a make-break switch actuated by said spindle, the improvement of a switch and speed control mechanism comprising,

a rotatable speed control shaft and cam means including,

a first cam on said shaft,

a cam follower actuated from a neutral position by rotation of said first cam and spring means acting on said governor system connected at one end to said follower to apply a force to said system to control said speed,

a second cam adjacent said first cam and rotatable therewith,

switch means operable by said second cam to control the power unit circuit,

said cams being angularly displaced for operation of said switch means to open the circuit when said cam follower is in neutral position,

said spring force balancing governor system including an arm connected by the spring means at the other end thereof to said cam follower, pivot means connecting said arm for low inertia movement thereof,

said arm being actuated by said spindle,

said arm being actuated by said spindle, whereby a variable spring force is applied to the governor system over at least part of the speed range and the spring force is increased on said make-break switch at higher tool speed.

2. Apparatus as described in claim 1 having a bracket secured to said casing,

said bracket having an insulated slider thereon contacted by said second cam,

said slider actuating said switch means to closed position on rotation of said speed control shaft to increase speed,

7 said bracket forming a support for said speed control shaft, and said cam means supporting said shaft on said bracket. 3. In an electric food mixer having a casing and a power unit therein including a force balancing governor system with a driven spindle controlled by said system and having a make-break switch actuated by said spindle, the improvement of a switch and speed control mechanism comprising,

a rotatable speed control shaft,

a cam on said shaft having a first cam surface thereon, a resilient cam follower actuated from a neutral position by said first cam surface on shaft rotation, a pivoted arm connected for actuation of said makebreak switch by said governor system, spring means connecting said follower and arm to apply a counterforce to said arm and control speed, a second cam surface on said cam axially and angularly displaced from said first surface, a second cam follower actuated by said second surface, switch means in the power unit circuit biased to closed position and operable independently by said second cam surface to control the power unit circuit, and means forming part of said spring means to change the spring force from variable to a solid nonresilient link at a predetermined shaft rotation, said angular displacement of said cam surfaces being disposed for operation of said switch means by said second cam surface to open the circuit when said resilient cam follower is in neutral position, whereby a variable spring force is applied to the governor system at low rotation of said shaft at low mixer speed and the solid linkage is applied upon brackethas an insulated slider thereon contacted by said secondcam surface, said slider actuating said switch means to closed position on rotation of said speed control shaft to increase speed.

7. Apparatus as described in claim 5 wherein said second cam follower is an insulated slider disposed on said bracket, said slider actuating said switch means for operation to closed position on rotation of said speed control shaft to increase speed.

References Cited UNITED STATES PATENTS 2,099,050 11/ 1937 Chamberlain 200- 2,671,192 3/1954 Fleming 318325 2,907,226 10/1959 Gasparotti 200-80 7 2,930,597 4/1960 Howell et al 318-325 X ROBERT K. SCHAEFER, Primary Examiner D. SMITH, 111., Assistant Examiner US. Cl. X.R. 318-325 

